Ceramic materials have been made and used for thousands of years. More recently, industrial processes have demanded higher performance materials for increased temperature, thermal efficiency, operating life times and more chemically corrosive environments. These demands have often been met by materials of higher density (to reduce chemical permeation) and purity (to eliminate low melting phases). While this has generally been successful, these denser, more pure materials are more prone to damage during thermal transients due to the relative ease of crack propagation in the dense materials as compared to the less pure, less dense materials. One way to obtain acceptable ceramics of high density is by combining two materials. One such successful ceramic is a composite of magnesia (MgO) and magnesium aluminum spinel (MgAl.sub.2 O.sub.4) which is fusion cast (poured into forms from the molten state.) The reduction in stress cracking is reported to be due to the gap which exists between the spinel matrix and the MgO grain, Smyth and Pollina, Refractory Oxides for MHD Heaters, HIGH TEMPERATURE SCIENCE 13, pp 189-217 (1980). The desired thermal shock and high temperature deformation resistance has not been generally available in non-fusion cast ceramics because sintering the oxide starting powders does not produce a material with the proper microstructure.
It would therefore be advantageous to have a technique and composition readily available to produce the observed effect without the difficulties inherent in fusion casting, such as the high temperatures employed, uncontrolled porosity and, shape and size limitations.